Manufacture of zinc oxid.



UNITED STATES PATENT oEEIcE.

FRANK G. BREYER, 0F PALMERTON, PENNSYLVANIA, JAMES A. SINGMASTER, 0F

BRONXVILLE, NEW YORK, AND ALBERT E. HALL, OF PALMER/ION, PENN- SYLVANIA, ASSIGNORS TO THE NEW JERSEY ZINC COMPANY, OF NEWYOR'K, N. Y., A CORPORATION OF NEW JERSEY.

MANUFACTURE OF ZINC OXID.

No Drawing.

To all whom it may concern:

Be it known that we, FRAN'K G. BREXER, a

citizen of the United States, residing at Palmerton, Carbon county, State of Pennsylvania, J AMES A. SINGMASTER, a citizen of the United States, residing at Bronxville, Westchester county, State of New York, and ALBERT E. HALL, a citizen of the United States, residing at Palinerton, Carbon county, State of Pennsylvania, have invent ed certain new and useful Improvements in the Manufacture of Zinc Oxid; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appeitains to make and use the same.

In the commercial production of zinc oxid (including leaded zinc oxid) by means of the so-called VVetherill process, it is customary to first charge upon the perforated grate bottom or hearth of the furnace a layer of buckwheat anthracite coal (which is thereupon ignited by the residual heat of the fur- H366) and by means of a forced draft to bring this initial layer of coal to well-developed combustion. Upon this ignition coal is then charged the customary mixture or working charge characteristic of the Wetherill process, that is to say, a mixture of finely-divided reducing coal with the finely-divided zinkiferous material, such as zinc silicate, roasted zinc blende, roasted socalled mixed sulfide of zinc and lead, or other reducible zinc-containing material at the disposal of the operator. The air blast beneath the perforated grate is continued, and, when the familiar flames of greenish tint, known as zinc candles, begin to make their appearance at the upper surface of the 'charge, indicating that the reduction and volatilization of the zinc and its oxidation to the form of fume is well under way, the products of combustion carrying the zinc oxid fume and other volatilized metallic compounds are conveyed through the cus tomarycooling flues, etc., to the bag-room wherein, in a cooled condition, they filter through the bags and pass off into the atmosphere, leaving the fume collected in the interior of the bags, from which it is removed at convenient intervals. The furnace operation is continued until the production Specification of Letters Patent.

Patented Nov. 18, 1919.

Application filed January 8, 1919. Serial No. 270,179.

of fume therefrom in appreciable quantity ceases, whereupon the residual charge, which is, to a large extent, sintered together, is broken up by long-handled rabbles and pried up and lifted or scraped out through the furnace doors into a receiving pit, or the like, preparatory to the startingof a new operation.

In practice, the above described furnace operation is attended with certain defects interfering with its full efficiency. Prominent among these defects is the inevitable tendency to the formation of blow-holes or craters at various regions of the charge. These blow-holes represent severally the paths of least resistance for the blast in its passage through the charge and to the extent to which they develop in the progress of the operation they interfere with the uniform distribution of the air in its upward passage and produce hot spots representing excessive temperatures as compared with other regions of the charge. From time to time, the workmen endeavor to eliminate these blow holes or hot spots, as far as is feasible, by rabbling the upper surface of the charge, thereby filling in the blow holes or breaking up their continuity; but in spite of the palliative effect of these expedients (which, moreover, consume considerable of the workmans time and attention it is impossible to obtain uniform working conditions throughout the entire extent of the charge;'so that there is not only waste of fuel, and the production locally of higher temperatures than is desirable, but the residues taken from the furnace at the termination of the operation contain notable percentages of zinc. The zinc contained in these residues cannot ordinarily be recovered commercially, and, whenthe residues are employed in the manufacture of spiegeleisen, which may be their destination, the presence of the residual zinc is even obj ectionable, for the reason that, when volatilized and oxidized in the'spiegeleisen furnace, it interferes to a greater or less extent with the normal furnace operation and tends to'collect in and obstruct the spiegeleisen furnace flues.

A further defect of the above described furnace practice is that the forced draft, which is employed under relatively considerable pressure, tends to project into the free space above the charge more or less dust, particularly in the region of the blow-holcs referred to, and this dusting is further aggravated by the rabbling operations; conse: quently, in addition to the metallic fume, the products of combustion carry with them from the furnace a notat-able proportion of dust in the form of fine particles of wire duced ore, carbon, ash, and the like, which tend to contaminate the fume proper and damage its color and marketability.

There are, furthermore, certain requirements of the practice of the WVetherill process as heretofore conducted which hamper the operator in the selection of the quality and size both of the coal and of the zinkifer ous material employed in making up the charge. Thus, the requirement that the charge shall be sufficiently permeable for the passage of the air, necessitates the use of a mixture of coal and zinkiferous material of a fairly coarse grade. Serious difficulties are encountered in the use of the smaller sizes of buckwheat coal; and only a fractional part of the zinkiferous constituents of the charge can consist of such extremely finely-divided materials as flotation concentrates, zinc precipitates, flue-dust containing zinc, or the like.

The present invention is designed to improve the practice of the lVctherill processparticularly in the respects noted. That is to say, to obtain a more uniform distribution of the air or other appropriate combustion supporting gas on its way through the charge; to lower the resistance of the charge to the passage of the air; to avoid the formation of blow holes or hot spots; to minimize the contamination of the fume by dust; to increase the permissible quantity of the working charge and consequently the amount of zinkiferous material treated in a given time period; to obtain a more complete extraction of the zinc and a saving of fuel per unit of zinkiferous material present; to effectively employ cheap coal of extremely small mesh and coal of such low grades as colliery washings, coke breeze, and the like; and to freely utilize zinkiferous material of any degree of fineness, including flotation concentrates, finely pulverulent ore, z'inc precipitates, flue dust, etc.

For the attainment of the improved results referred to, we have radically modified the present commercial practice of the lVetherill process. Thus, for the initial step of charging the grate bottom or hearth of the VVetherill furnace with a layer of fine ignition fuel, we have substituted a layer or bed of ignition fuel in the form of briquets. We have found, in actual practice, that it is feasible to employ, as the ignition or bed fuel, briquets prepared by compressing finely divided coal, together with a suitable binder (preferably the concentrated waste sulfite liquor of the sulfite paper pulp industry), and that the coal appropriate for the purpose may consist of the cheaper and smaller grades, as, for instance, anthracite coal below the No. 3 buckwheat size,-such as No. 4 buckwheat, colliery washings (dirtl coalor dust coal), coke breeze, etc We have found that, for this ignition or bed fuel, it is suitable to employ briquets of such size and shape as to materially reduce the resistance to the air, and nevertheless to supply such a substantially uniform substratum for the support of'the supen posed working charge as to give free access and practically equal distribution of the air thereto. Thus, the ignit In or bed fuel briquets may be made of a form approximating two pyramids having a common rectangular base of say 11 inches on each side,

i the thickness of the briquets from the apex of one pyramid to the other being say 1% inches. We have ascertained that when, instead of the usual layer of buckwheat anthracite coal, a layer or bed of these briquets is charged upon the grate bottom or hearth of the VVetherill furnace as ignition fuel, the briquets will become ignited by the residual heat of the preceding charge and that they may then be brought to well developed com bustion appropriate to the reception of .the working charge, and that when thus brought to well developed combustion, the working charge may be supplied, without substantially disturbing the original distribution of the ignition briquets. and, consequently, with the preservation of the fairly uniform air passages which the ignition briquets provide over the entire surface of the hearth for the upward passage of the blast into the working charge. In some instances, such a percentage of zinkiferous material may be incorporated in the ignition briquets as may be tolerated without substantially interfering with their normal function, and, to the eX- tent to which this is permissible, the ignition briquets will add a reducing function to their normal ignition function.

A second characteristic feature of the invention consists in making up the working charge of the furnace (that is to say, the reducing agent and the zinkiferous or zinkiferous and plumbiferous material) in the form of briquets. This feature of the invention may be practised either by briqueting the zinkiferous material alone, without briqueting the reducing agent charged with it; or by briqueting the reducing agent and not hriqueting the zinkiferous material; or by briqueting the reducing agent andbriquoting the zinkiferous material separately therefrom; or, preferably by briqueting a mixture of the reducing agent and of the zinkiferous material. These briquets may be made of the "same shape and dimensions as the fuel briquets hereinbefore referred to, and by the employment of any suitable binder, such as the concentrated waste sulfite liquor described. The reducing agent employed may be of any suitable kind, but one of the marked advantages of the briqueting is that it permits, as we have ascertained, the effective and economical use of reduction coal of the cheaper grades and finer mesh, such as anthracite coal of finer mesh than No. 3 buckwheat, colliery washings, coke breeze, and the like. A typical procedure for the production of the briquets made from the preferred mixture of reduction coal and zinkiferous material is as follows:

The reduction coal (as, for instance, anthracite dust or slush) which usually averages from -70% of carbon (and which usually has a moisture content of about 10%) is placed, together with the sulfite liquor, in a revolving mixer of the kind employed for the mixing of concrete and, after a short period of mixing, the linkiferous material is added, the mixing operation then continued for a further period of three minutes or more. Thus, for 800 pounds of the anthracite dust or slush coal, 6? pounds of concentrated waste sulfite liquor of 30 Baum is employed, and the .zinkiferous material added may consist suitably of 960 pounds of finely crushed zinc ore averaging say 20% of zinc oxid and 16% silica, together with 480 pounds of socalled dust ore averaging say 23% of zinc oxid and 8 to 9% sil1ca,--these ores being, in this instance, mixtures consisting mainly of silicate of zinc, Franklinite and calcite and carrying usually from 1 to 6% of moisture. From the mixer, our practice has been to dump the material directly into a 5 foot dry pan Chilean mill located directly below, and to subject it to the mixing and comminuting action of the mill for three minutes or more. From the Chilean mill, the material is taken to the briqueting press. The form of press that we have used to advantage consists of cooperating rolls about 20 inches in diameter and provided with cooperating molding pockets, so that when the material is fed into the pans of the rolls from above, it is molded into briquets having the shape and dimensions hereinbefore referred to and weighing in the neighborhood of three ounces. The two rolls of the briqueting machine are held together by heavy spring pressure so as to exert a compressive force upon the material as it is eing formed into the briquets of about 2,000 pounds to the square inch.

The briquets (averaging between 5% and 10% moisture for the mixed charge and up to say 15% moisture for ignition fuel briquets)..are placed in baskets which may conveniently be 30 inches long, 20 inches Wide and 4: inches high,the sides of the baskets being of heavy sheet iron and the bottoms of inch wire mesh. In these baskets, or in similar receptacles, We dry and bake the briquets as, for instance, by mounting the baskets filled with briquets upon buggies carrying say twelve baskets in four tiers of three baskets each, which are thenpushed into a tunnel drier of the direct coal-fired type. The briquets remain in the drier from one to two hours, at a temperature of approximately 200 C. dependent upon the rate of firing. The dried briquets are then removed from the drier, cooled and stored, under cover, for subsequent use. This drying and baking of the briquets is of service to impart to them the desirable amount of resistance to crumbling and breaking, so that they may be freely subjected to the rough handling incident to storm them, conveying them to the furnace, and incident to charging them into the furnace either by hand or otherwise, and so that they may likewise substantially maintain their form during the period that they are giving off their zinc in the furnace.

lVhile some of the advantages of the invention may be attained by briqueting either the reducing agent or the zinkiferous material (or both of them) separately, our preferred practice as above noted, is to make the briquets of a mixture of the reducing agent and the zinkiferous material. So also,whi1e the working charge, partly or wholly briqueted, may be used in conjunction with an ignition layer of fine anthracite coal, we prefer to use briqueted ignition fuel in conunction with a briqueted workingcharge made up of a briqueted mixture of reducing agent and zinkiferous material.

Thus, we have found that when, as in our preferred practice, the working charge, in the form of briquets made up of a mixture of zinkiferous material or zinkiferous and plumbiferous material and reducing'coal, is charged upon a layer of ignition coal briquets of like shape and dimensions, all of the advantages hereinbefore recited as incident to the invention are present. In other words, the supplying of the working charge of briquets .upon the sul stratum of well ignited ignition briquets in full combustion, builds up within the furnace a total charge of such low resistance to the upward passage of the air, that the pressure of the blast in the ash pit may be very materially lowered; or, in some cases, it may be supplanted by the suction effect of the ordinary exhaust fan employed in the \Vetherill process for withdrawing the fume from the furnace, this exhaust sufiioing to pull through the charge a suflicient volume. of air appropriate for the operation.

The process proceeds, without the pr0 duction of craters or hot spots and with an even distribution of the air over the entire extent. of the chargel It is also found that the reduction and volatilixation ot' the zinc, its oxidation. and its recovery as fame, to gether with whatever lead or other oxidizable metallic compounds are present. proceeds more completely than in the ordinary practice of the \Yetherill process, and that. the residues show a materially lessened loss of zinc.

As a typical instance of the practice of the invention. 900 pounds or ignition coal briquets (which may consist entirely of dust coal) are spread out as evenly as possible upon a \Vetherill grate of 111 square ft. area. These briquets are then ignited by the residual heat of the furnace from a former operation. and when they have reached a gmd yellow heat. we. charge upon them 8,U00 pounds of briquets made from the mixture of reducing coal and Zinkiferous material.

A much lighter blow is used. as the process proceeds, than with the usual lVetherill furnace charge. The residues are withdrawn in from (3 to 12 hours, the 8 hour period usually giving the best results. The same number of operators is used for with drawing the residues as for the ordinary 6,000 pound ll'ethrill charge. so that for the same labor the charge treated may be increased 0ne-third. It is also found that the clinker adheres with very much less tenacity to the furnace walls. so that the exertion required for breaking up the clinker and removing it from the furnace is correspondingly less arduous.

e have hereinbefore referred to the increased capacity of output incident to the invention; and, in this connection. we may state that in the preferred practice of the invention wherein briquets are used for the, ignition coal and briquets of mixed Ziltl\'lfe1 ous material and reduction coal are used, we. have been able, with the same expenditure of fuel to obtain a higher extraction of Zinc (leaving less zinc in the residue) than in the ordinary etherill process, and that for a furnace run of the same time-period normally employed in working off the charge of a VVetherill :t'urnace, we have been able as hereinbefore particularly noted, to treat a briqueted charge containing as high as onethird more. of zinltiferous material than is contained in the normal lVetherill working charge.

It will. of course. be understood that the specific examples of typical means of practising the invention are. to be understood as illustratire of its practical aprflhmtion, and that they may be widely varied without departing from the intended scope of the invention more broadly set forth in the gene a1 description and in the claims hereunto annexed.

By the expression Wet'herill process, as we have. used the same herein. 1s to be understood the furnacing step of the process for producing zinc oxid or leaded zinc oxid, as a finished commercial product, or as a zinc oxid (or zinc-lead) concentrate. or in any other form, in which a charge of the zinkiferous (or zinki't'crous and plumbiferous) material mixed with a reducing agent and spread on an ignited bed of fuel is subjected to a combustion supportil'ig blast or draft and brought to a sutliciently high temperature to reduce the compounds of zin' and olatilizc the reduced metal (and to reduce and (or) volatilize the compounds of lead when present) without bringing the charge to a. condition where it becomes impervious to the blast or draft; the entire charge being supported on a furnace hearth or grate designed to hold it without letting any considerable part. drop through and the workedotl material being discharged as a clinker or cimler. The "furnacing step is independent of the subsequent treatment of the laden furnace gases and of the collection of the zinc oxid or leaded zinc oxid.

hat. we claim is:

1. 1n the production of zinc oXid or leaded zinc oxid by the \Vethcrill process, the step of supplying the bed fuel to the furnace hearth in the form of briquets; substantially as described.

In the production of zinc oxid or lead ed lzinc oxid by the \Vetherill process, the step of supplying the bed fuel to the furnace hearth in the form of briquets, said briquets containing a percentage of zinkiferous 0r zinltiferous and plumbiferous material; substantially as described.

3. In the production of zinc oxid or leaded zinc oxid by the l'Vetherill process, the step of supplying in the working charge briqueted zinkiferous or zinkiferous and plumbiferous material; substantially as described.

4. In the production of zinc oxid or leaded zine oxid by the W'etherill process, the step of supplying in the working charge briqueted reducing material; substantially as described.

5.. In the production of zinc oxid or leaded zinc oxid by the VVetherill process, the step of supplying in the working charge a briqueted mixture of zinkiferous or zinkiferous and plurnbiferous material and reducing agent; substantially as described.

6. In the production of zinc oxid or leaded zinc oxid by the VVethcrill process, the step of supplying the bed fuel in the form of briquets together with the step of supplying in the working charge briqueted 'zinkiferous or zinkiferous and plumbiferous material; substantially as described.

7. In the production of zinc oxid or lead ed zinc oxid by the VVetherill process, the

step of supplying the bed fuel in the form of briquets, together with the step of supplying in the working charge b'riqueted reducing nnrteriul; substantially as described.

e. In the production of zinc oxid or lead ed zinc oxid by the \Vetherill process, the step of supplying the bed fuel in the l'orin of briquets, together with the step of supplying in the working charge a briqueted mixture of zinkii'erous or zinkiferous and pluinbiferous material and reducing agent; substantially as described.

9. In the production of zinc oxid or leaded zinc oxid byv the \Vetherill process, the step of supplying the bed fuel in the form of briquet-s, said briquets containing a percentage of nietalliferous material, together with the step of supplying in the working charge briqueted zinkiferous or zinkiferous and plumbiferous material; substantially as described.

10. In the production of zinc oxid or leaded zinc oxid by the Wetherill process, the step of supplying the bed fuel in the form of briquets, said briquets containing a percentage of metalliferous material, together with the step of supplying in the working charge briqueted reducing material; substantially as described 11. In the production of zinc oxid or lead ed zinc oXid by the W etherill process, the

step of supplying the bed fuel in the form of briquets, said briquets containing a percentage of metalliferous material, together with the step of supplying in the working charge a briquetedmixture of zinkiferous or zinkiferous and plumbiferous material and reducing agent; substantially as described.

d2. In a process for producing zinc oxid or leaded zinc oxid involving the blowing of air into a bed containing the metal-bearing material and combustible material under conditions which will leave the worked-off charge as a clinker and which will produce a volatile fume, the step of supplying at least part of the charge in the form of briquets; substantially as described.

In testimony whereof we afiix our signatures.

FRANK G. BREYER. JAMES A. SINGMASTER. ALBERT E. HALL 

